A conventional signal transmission device that divides transmission data into data about the safety of an elevator and other data, and creates a packet which is a combination of plural pieces of data including at least the data about safety and then transmits the packet is disclosed (for example, refer to patent reference 1). This device adds a CRC (Cyclic Redundancy Code) to the above-mentioned data about safety (referred to as the safety data from here on) to enable a receive side to detect a transmission error by using the CRC and make a request for retransmission of the transmit side when detecting a transmission error, thereby being able to transmit the safety data about the safety of the elevator certainly and promptly.
However, in such a conventional signal transmission device as disclosed by patent reference 1, a CPU carries out a process of retransmitting the safety data in response to the request sent thereto from the receive side. This CPU serves also as a unit for handling the safety data which are received. A problem is therefore that when a delay time permitted in the transmission of the safety data is short, such as when the transmission time interval of the safety data is short, the next-time transmission of the safety data may be delayed because of the processing load and this delay may exceed the permissible delay time if the CPU which also handles the safety data performs the retransmitting process in order to transmit the safety data certainly.
The present invention is made in order to solve the above-mentioned problem, and it is therefore an object of the present invention to provide a signal transmission device for elevator that can transmit safety data promptly by carrying out continuous transmission of the safety data and a process of handling the safety data independently of each other.